Generalized Equivalent Circuit Model of MMC-HVDC for Power System Simulation

Abstract

A method to simulate a circuit includes receiving at least one circuit requirement and at least one Modular Multilevel Converter (MMC) parameter; determining an operating mode and switching states of an arm circuit; determining each capacitor current based on the switching states and an arm current; determining capacitor voltage and arm voltage; and generating an equivalent circuit model to simulate MMC-based HVDC systems and DC grids in a hybrid AC and DC power system.

Description

TECHNICAL FIELD[0001]This invention relates to an efficient model of Modular Multilevel Converters (MMCs), which is based on the generalized equivalent circuit for high-voltage direct current (HVDC) systems.BACKGROUND[0002]MMCs have become the basic building block for multi-terminal dc (MTDC) systems and dc grids. Due to modularity and scalability, the MMC becomes the most attractive converter topology for medium / high voltage applications, especially for voltage-sourced converter high-voltage direct current (VSC-HVDC) transmission systems. Large-scale MMCs-embedded power systems need to investigate dynamic performance, fault, protection, and stability. The efficient model of MMC is one of the main challenges associated with the study of large-scale MMC-based power systems.[0003]To analyze large-scale hybrid ac and dc power systems, modeling and simulation plays an important role in investigating system dynamics under various operating conditions, i.e., startup, normal, transient, an...

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Benefits of technology

[0006]In another aspect, a generalized equivalent circuit model (ECM) is used for modeling and simulating the MMCs based on various SM circuits and arm configurations under different operating conditions. A generalized arm equivalent circuit is used to model and simulate various MMCs under startup / precharging, normal, and fault conditions. The ECM considers all internal states and can be used to investigate internal dynamic control strategies, e.g., capacitor voltage balancing strategies. To further improve simulation efficiency, the reduced-order ECM is derived by neglecting the dynamics of individual capacitor voltage and considering the average capacitor voltage. The modeling technique can efficiently and accurately model and simulate the MMC-HVDC systems based on various SM circuits and arm configuration under different operating conditions.

[0007]The equivalent circuit model (ECM) can significantly improve simulation efficiency and be applied for precharging, normal, and fault operation analysis of the MMC-HVDC systems while considering the behaviors of various SMs. This invention can also be used to investigate internal dynamics based on various control strategies, e.g., capacitor voltage balancing, when full states are considered.

Problems solved by technology

The efficient model of MMC is one of the main challenges associated with the study of large-scale MMC-based power systems.

However, it is time consuming and infeasible to model and simulate large-scale MMCs-embedded power systems with detailed switching model (DSM).

However, detailed DSM modeling is time-consuming and infeasible due to a large number of semiconductor switches in high-level systems.

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